Broadband networks are systems of network components which receive and/or transmit broadband signals where the signals are analog waveforms within the 5 MHz (megahertz) to 1 GHz (gigahertz) frequency range; contain information encoded with analog modulation; and are combined through multiplexing (typically, frequency division multiplexing). These network components are interconnected through network connections. Examples of broadband networks include CATV/MATV (Community Access Television, Multiple Access Television) systems and data networks. A CATV/MATV system is typically composed of one or more "head-ends" which deliver television channels to a community of homes over an HFC (hybrid-fiber coax) infrastructure. The network components in a CATV/MATV broadband network include RF (radio-frequency) modulators, RF demodulators, frequency converters, band-pass filters, band-trap filters, combiners, splitters, taps, attenuators, equalizers, amplifiers, broadband switches, fiber-optic nodes, and metering equipment. These components are connected to each other through transmission lines which are typically coaxial cable.
Combiners and splitters perform complementary functions. Combiners sum two or more inputs which pass a range of frequencies to a common output. Inputs and outputs must have an electrical impedance that matches the source (input) or load (common output) over the combiners range of frequencies for the most efficient transfer of signal power. At the same time electrical isolation must be maintained between the inputs so that one input source does not pick up or transmit unwanted signal to any other input source. The splitter provides the complementary function of distributing a signal source at a single input to two or more outputs. The same impedance and isolation is required. See "Understanding Power Splitters . . . " published by Mini-Circuits and the CD22100 data sheet published by Harris Semiconductors which are herein incorporated by reference in their entirety.
The CATV/MATV systems are said to be broadband networks because the information which flows between the CATV/MATV network components is encoded in analog signals within the 5 MHz to 1 GHz range. The RF modulator components receive analog or digital signals containing information (such as audio and video information or digital data) in the baseband spectrum (below 5 MHz) and modulate the signals into the broadband spectrum. Each individual RF modulator will typically restrict the modulation of its input signals to within a six megahertz band, or television channel, of the broadband spectrum. Television channel 2, for instance, is the band of broadband spectrum between 54 MHz and 60 MHz. A television channel 2 modulator will modulate its audio and video into this range so that a connected television receiver (demodulator) can receive it. Demodulators listen to network connections for modulated signals within the broadband spectrum and convert the modulated signal into one or more demodulated output signals. The frequency range which the demodulators listen to is typically coordinated with the frequency range that one or more modulators are broadcasting on so that a demodulator tuned to the spectrum range of 54 MHz to 60 MHz (channel 2), for instance, will demodulate and output the signals (such as audio and video or data signals) which were modulated by a connected channel 2 modulator. A fiber-optic node is another network component which generates and receives broadband information. These nodes up-convert signals on a given range of the broadband spectra (such as 5 MHz to 50 MHz) into the optical frequency spectrum for transmission over optical media such as fiber-optic cable. The nodes can also receive signals on a given range in the optical frequency spectrum and down-convert the signals into the broadband spectrum for transmission over a broadband network. Fiber-optic nodes are often used to interconnect with optical fiber, two or more broadband networks which are separated over long distances.
Many of the network components are directional in nature, that is, they receive broadband signals, perform a function over the broadband spectrum, and retransmit the altered signals. Frequency converters translate the signals in a given range of the broadband spectrum into a second range of the broadband spectrum. Amplifiers are used to rejuvenate signals which have decayed due to transmission losses. Band-pass filters attenuate signals (typically noise) in a given range of the broadband spectrum and attenuators attenuate signals over the entire broadband spectrum. Equalizers compensate for frequency dependent decay of signals over long distances of transmission lines (network connections).
Broadband networks are often used in a bi-directional manner. Through frequency multiplexing, for instance, the broadband spectrum is often segmented into forward and reverse frequencies. One standard used in CATV/MATV systems is that the frequencies from 54 MHz to 750 MHz are used as forward frequencies and the frequencies within 5 MHz to 50 MHz are used for return information. CATV/MATV head-ends will broadcast television channels such as channel 2 (54-60 MHz) in the forward frequencies to their subscribers homes and receive data from the subscribers in the return frequencies. Data from the subscribers can be video signals modulated to a television channels (such as a video signal from a town-hall or sports event), information sent from individual subscriber's set-top boxes, or digital computer information sent from cable modems. Typically, return transmissions from the subscribers are coordinated through time-domain-multiplexing so that a transmission (television channel, set-top box signal, digital data signal) from one subscriber will not interfere with a transmission from another.
In broadband networks we want to switch and isolate different network connections so that the same broadcast network can be used to communicate between any one or more points to any other points. i.e. traffic (bandwidth) management can be done by combining network connections with limited bandwidth needs together and isolating networks connections with high bandwidth requirements. As the number of RF connections to be switched increases the difficulty of maintaining isolation also increases. This is because the RF signal conductors must be in close proximity for the various switching combinations to take place. However, it is this proximity which causes the conditions for RF leakage of unwanted mixing of signals.
Common matrix switching is done point to point, that is each input connects to only one output. The user is assured one source will be loaded by one and only one load. In generally known point to point switching systems, combining more than one input to an output is, by definition, not possible. Nor is splitting of a single input into more than one output. Further, common matrix switches cannot combine separate bands of different frequencies on multiple inputs into a single band of different frequencies on one or more outputs.